1. Field of the Invention
Embodiments of the present invention generally relate to substrate processing apparatuses and methods, such as apparatuses and methods for flat panel display processing (i.e. LCD, OLED, and other types of flat panel displays), semiconductor wafer processing, and solar panel processing. In particular, the embodiments of the invention relate to sputtering target for large area substrate processing systems.
2. Description of the Related Art
Physical vapor deposition (PVD) is one of the most commonly used processes in fabrication of electronic devices, such as flat panel displays. PVD is a plasma process performed in a vacuum chamber where a negatively biased target is exposed to a plasma of an inert gas having relatively heavy atoms (e.g., argon) or a gas mixture comprising such inert gas. Bombardment (or sputtering) of the target by ions of the inert gas results in ejection of atoms of the target material. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate pedestal disposed underneath the target within the chamber. Flat panel display sputtering is principally distinguished from the long developed technology of wafer sputtering by the large size of the substrates and their rectangular shape.
FIG. 1 (prior art) shows a typical DC magnetron PVD reactor 10, which includes an electrically grounded vacuum chamber 12 to which a target 14 is vacuum sealed through an electrical isolator 16. A DC power supply 18 negatively biases the target 14 with respect to the chamber 12 to excite an argon sputter working gas into a plasma. However, it is noted that RF sputtering is also known. The positively charged argon ions are attracted to the biased target 14 and sputter material from the target 14 onto a substrate 20 supported on a pedestal in opposition to the target 14. A magnetron 24 positioned in back of the target projects a magnetic field parallel to the front face of the target 14 to trap electrons, thereby increasing the density of the plasma and increasing the sputtering rate. In modern sputter reactors, the magnetron may be smaller and be scanned about the back of the target 14. Even a large magnetron may be scanned in order to improve the uniformity of erosion and deposition. Aluminum, titanium, and copper targets are typically formed of a sputtering layer of the material to be sputtered coated onto or bonded to a target backing plate of less expensive and more readily machine-able material.
Sputter reactors were largely developed for sputtering onto substantially circular silicon wafers. Over the years, the size of silicon wafers has increased in diameter from 50 mm to 300 mm. Sputtering targets need to be somewhat larger than the wafers to provide more uniform deposition across the wafer. Typically, wafer sputter targets are formed of a single circular member for some materials such as aluminum and copper or a single continuous sputter layer formed on a backing plate for more difficult materials.
In the early 1990's, sputter reactors were developed for thin film transistor (TFT) circuits formed on glass panels to be used for large displays, such as liquid crystal displays (LCDs) for use as computer monitors or television screens. The technology was later applied to other types of displays, such as plasma displays and organic semiconductors, and on other panel compositions, such as plastic and polymer. Some of the early reactors were designed for panels having a size of about 400 mm×600 mm. Because of the increasing sizes of flat panel displays being produced and the economy of scale realized when multiple displays are fabricated on a single glass panel and thereafter diced, the size of the panels has been continually increasing. Flat panel fabrication equipment is commercially available for sputtering onto panels having a minimum size of 1.8 meter and equipment is being contemplated for panels having sizes of 2 m×2 m and even larger. One drawback of a single-piece target is the price of the target as the size of the target increases. Bonding multiple tiles of sputtering materials to a single target backing plate is an economical alternative.
Combining sputtering target tiles to create a larger sputtering target without gaps raises many challenges. Therefore, a need exists in the art for a method of combining sputtering target tiles to create large sputtering target for large area substrate processing systems.